1. Field of the Invention
The present invention relates to the field of display technology, and in particular to a thin-film-transistor (TFT) substrate structure and a manufacturing method thereof.
2. The Related Arts
Amorphous silicon (a-Si) is the most widely used semiconductor material in the semiconductor industry. The a-Si material shows a great potential difference when put in contact with metals, making it hard to form an ohmic contact. In practical applications, in order to make an ohmic contact between a metal and a semiconductor, it is commonplace to heavily dope element P in a surface of the semiconductor for lowering the contact resistance between the metal and the semiconductor and increasing current efficiency.
FIG. 1 is a schematic view, in a sectioned form, showing a conventional thin-film transistor (TFT) substrate structure. The TFT substrate structure comprises a base plate 100, a gate terminal 200 formed on the base plate 100, a gate insulation layer 300 formed on the base plate 100 and covering the gate terminal 200, an amorphous silicon layer 400 formed on the gate insulation layer 300 to be located above and correspond to the gate terminal 200, and a source terminal 500 and a drain terminal 600 formed on the gate insulation layer 300 and respectively contacting two side portions of the amorphous silicon layer 400. The amorphous silicon layer 400 comprises a channel zone 450 formed therein to correspond to the gate terminal 200. The amorphous silicon layer 400 has a surface that is formed with first and second N-type heavily-doped zones 410, 420 respectively corresponding to two sides of the channel zone 450. The source terminal 500 and the drain terminal 600 are respectively set in contact with the surfaces of the first and second N-type heavily-doped zones 410, 420.
FIG. 2 is a curve illustrating a leakage current Ioff of an a-Si device involving the TFT substrate structure of FIG. 1 varying with a gate voltage Vg. It is known from FIG. 2 that certain problems exist when an operation current (Ion) of the TFT substrate structure is increased. When the loading voltage reaches a predetermined level, positive charges are induced so as to generate a hole-conducting channel. The leakage current (Ioff) is thus increased, making the curve severely bent and leading to a reliability issue.
Thus, it is desired to provide a TFT substrate structure and a manufacturing method thereof that overcome the above problems.